(a) Technical Field
The present disclosure relates, generally, to a method for forming an inverter circuit. More particularly, it relates to a method for forming a capacitor module circuit in an inverter for driving a drive motor of an electric vehicle.
(b) Background Art
A hybrid vehicle is generally meant to refer to a vehicle driven by efficiently combining at least two different types of power sources. In most cases, the hybrid vehicle is driven by an engine (e.g., an internal combustion engine) which generates a rotational force by burning fuel (e.g., fossil fuel such as gasoline) and an electric motor which generates a rotational force with the electric power of a battery. Such an exemplary hybrid vehicle is typically referred to as a hybrid electric vehicle (HEV).
The hybrid vehicle is driven in an electric vehicle (EV) mode, which is directed to a pure electric vehicle mode using only the power of the electric motor (or drive motor), in a hybrid electric vehicle (HEV) mode, which is an auxiliary mode using the rotational force of the drive motor as an auxiliary power source with the use of the rotational force of the engine as a main power source, or in a regenerative braking (RB) mode, in which braking energy or inertia energy of the vehicle produced by braking or during driving by inertia is recovered by power generation of the drive motor and charged in a battery.
A hybrid vehicle typically includes a battery (e.g., a high voltage battery), which repeats charge and discharge during operation of the vehicle to supply electric power required for driving the drive motor, and an inverter for rotating the drive motor by the power of the battery.
The battery supplies required electric power and is charged with electric power generated by the drive motor during regenerative braking, and the inverter inverts the phase of the electric power supplied from the battery to operate the drive motor.
In particular, the inverter is a power converter for operating the drive motor and charging the battery. The inverter converts the electric power of the battery to operate the drive motor for power assist and converts the electric power during regenerative braking to charge the battery.
FIG. 1 is a schematic diagram showing exemplary connection relationships between a battery 1, an inverter, and a drive motor 2. As shown in FIG. 1, the inverter comprises a capacitor module 11 including a plurality of capacitors C, which are related to the electromagnetic wave performance, such as EMI. EMC and the durability of the battery, a power module 12 including a plurality of switching elements S (e.g., Insulated Gate Bipolar Transistors (IGBTs)) for power conversion and a plurality of diodes D (e.g., free wheeling diodes, FWDs), a control unit (not shown) for controlling motor torque and speed, and current sensors 13 for measurement of the u-phase, v-phase, and w-phase currents required for the control.
Recently, with the development of power switching elements, the on/off switching speed of the element is suitably increased and, since the inverter as well as the drive motor is mounted on a vehicle chassis, the switching noise is spread over the entire vehicle during operation of the inverter, which has an effect on vehicle control units and, further, on the vehicle radio reception performance. As a result, a variety of methods for reducing the noise have been studied.
The switching noise generated by the inverter is transmitted to the vehicle chassis via a mounting bracket of the inverter and via the drive motor.
According to prior art methods for reducing the electromagnetic switching noise, a neutral point of a Y-capacitor in a capacitor module of an inverter is connected to a vehicle chassis to suppress the switching noise.
In one example of a method of using the Y-capacitor in the inverter, Japanese Patent Publication No. 2002-078352, incorporated by reference in its entirety herein, discloses a method for protecting an inverter device in which a Y-capacitor is used to remove common mode noise. Japanese Patent Publication No. 2001-045767, incorporated by reference in its entirety herein, discloses an inverter device in which leak current is reduced by feeding a canceling current from an AC neutral point of a Y-capacitor to an earth point via a secondary core of a transformer. U.S. Pat. No. 7,561,389, incorporated by reference in its entirety herein, is directed to an AC voltage output apparatus which reduces noise using a Y-capacitor.
FIG. 2 shows an exemplary inverter comprising a capacitor module 11 including a smoothing capacitor C3 and Y-capacitors C1 and C2 and a power module 12 as a switching noise source.
Preferably, the capacitor module 11 in the inverter using the Y-capacitors C1 and C2 to suppress switching noise has the following functions.
The capacitor module 11 has a smoothing function to suppress a rapid variation of voltage/current of a DC input terminal of the inverter by absorbing a high ripple current generated during the operation of the inverter (differential mode noise suppression). This smoothing function is performed by the smoothing capacitor C3 to allow the inverter to normally operate and, in particular, to increase the durability of a battery 1.
The capacitor module 11 also suppresses common mode noise, which is performed by the Y-capacitors C1 and C2 connected to the smoothing capacitor C3 in parallel in the capacitor module 11.
The ripple current absorbed by the smoothing capacitor C3 is a high current (e.g., more than 50 A), which is suitably consumed by heat generation in the smoothing capacitor C3, and is insulated from the vehicle chassis.
Although the current of switching noise components generated during the operation of the inverter and flowing through the Y-capacitors C1 and C2 in the capacitor module 11 is an extremely low current (e.g., less than 1 mA), it contains a high frequency component, and thus has a significant effect on the electromagnetic wave performance of the inverter and the vehicle. Typically, the specification of the Y-capacitor is determined to have a capacitance which exhibits excellent electromagnetic wave performance from the samples prepared by changing the capacitances of the Y-capacitors.
However, the capacitances of the Y-capacitors C1 and C2 are determined by an experimental approach, not by an analysis and forecasting method. Therefore, it results in a considerable loss of manpower and time, and a considerable cost is incurred to prepare the samples.
Further, the switching noise generated during the operation of the inverter may be transmitted to the drive motor 2, and the switching noise transmitted to the drive motor 2 is delivered to the vehicle chassis, thus causing the problems due to the switching noise. However, there does not appear to be a solution to the switching noise transmitted to the drive motor 2.
Accordingly, there remains a need in the art for capacitor module circuits in an inverter for driving a drive motor of an electric vehicle.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.